The present invention relates to a hydraulic cam shaft advance and retard mechanism and more particularly to such a mechanism which advances and retards the cam shaft of an engine, such as an internal combustion or diesel engine, in response to speed of the engine or other prescribed characteristics. The invention is also applicable to other mechanisms in which one rotating member is to be rotated synchronously or at prescribed timing variations with respect to a second rotating member while torque is being continuously transmitted between the two members.
In a typical internal combustion or diesel engine, the mechanism which controls the introduction of the fuel/air mixture into the cylinder and which controls the emission of exhaust gases from the cylinder is coupled to the engine crankshaft through a system of gears, chains, or belts and cams or equivalent means. Thus, in the absence of suitable adjustment means, the timing of the fuel/air mixture introduction into the cylinder and exhaust emission (determined by the cam shaft) with respect to piston position (which controls the crankshaft) is fixed by the design parameters of the engine. However, such engines operate much more efficiently if the timing of the cam shaft with respect to the crankshaft can be varied responsive to changes in engine speed or other operating characteristics. Thus, it is generally desirable to close the fuel intake valves earlier at low speeds to prevent the fuel and air mixture from being blown back through the intake valve. Conversely, at high speeds it is generally desirable to retard the operation of the fuel intake valve, because if the valve closes too quickly, the amount of fuel/air mixture delivered to the combustion chamber may be inadqeuate for maximum performance. Therefore, it is desirable to be able to vary the timing of the operation of the intake valves during the operating cycle. The intake valves are conventionally controlled by the engine cam shaft, which is in turn driven by the engine crankshaft. Thus, in order to vary the timing of the opening and closing of the intake valves, the relative rotational position of the cam shaft with respect to the drive or crankshaft must be capable of adjustment during the operation of the engine.
It is toward this general concept of cam shaft timing adjustment that the present invention is directed. This concept has been recognized before and has been approached in several ways. First of all, in U.S. Pat. Nos. 2,861,557 to Stolte and 4,091,776, to Clemens et al, there is illustrated and described a cam shaft timing control device in which the connecting member between the drive shaft and cam shaft includes a plurality of cooperating vanes. One set of vanes is connected to the drive member (crankshaft) and the other set of vanes is connected to the driven member (cam shaft). As ignition begins and rotation of the crankshaft commences, oil pressure is admitted to a chamber between adjacent vanes and a buildup of such pressure causes the vanes to separate, thereby creating a rotational adjustment of the cam shaft with respect to the drive shaft. Because of close tolerances which must be maintained and the volume of oil which must be circulated to operate the vanes, these devices are very expensive. Further, the size of these devices is such that they cannot fit existing domestic automotibles without significant alteration thereto.
In another approach illustrated and described in U.S. Pat. No. 3,721,220 to Garcea, the connecting member between the cam shaft and the drive shaft includes a plurality of arcuately shaped, intermeshed members which are initially separated a prescribed distance by a hydraulically operated ball stop. As engine speed increases, the amount of fluid delivered to the hydraulic ball stops is varied, thereby causing a displacement of one set of arcuate members with respect to the other. This displacement translates into a change in the rotational relationship between the cam shaft and drive shaft, thereby creating advance or retard timing. This device is believed to be designed to operate with separate cams for intake and exhaust valves and would not operate on single cam designs of more than four cylinders, because of the hydraulic pressure which would be necessary to operate pistons 22. In another series of patents, namely U.S. Pat. Nos. 3,401,572 to Bailey; 4,302,985 to Natkin; and 4,421,074 to Garcea et al, the crankshaft and cam shaft are connected by a coupling which includes a piston moved axially by means of hydraulic pressure. The piston rides on a helical spline attached to one or other of the crankshaft or drive shaft. Thus, the axial movement of the piston causes a relative rotations displacement between the drive shaft and crankshaft.
Finally, another series of patents, namely U.S. Pat. Nos. 3,626,720 to Meacham et al; 3,685,499 to Meacham et al; and 3,827,413 to Meacham, each illustrate and describe a timing control device which is somewhat similar to the series of patents identified in the paragraph immediately hereinabove. The exception here is that a helical ball spline connects the driven member (cam shaft) with the driving member (crankshaft). The helical ball spline will thus reduce the frictional drag which might be attendant to the use of merely a helical spline.
While each of the approaches set forth above result in a cam shaft timing control, they have achieved varying degrees of success, and are in general relatively complicated and expensive to effect. For example, many of the devices utilize a heavy spring to normally bias the cam shaft in one direction or the other. When the hydraulic pressure (bias) is then removed, the heavy spring may or may not perform as designed to overcome the frictional drag on the engine and return the cam shaft to the normal or home position. Also, most, if not all of the prior art discussed hereinabove require a major modification to the cam shaft in order to effect the control coupling which must be mounted between the cam shaft and the crankshaft.
In the present invention, however, a different approach is used which is designed to eliminate the problems and complicated mechanisms described hereinabove. The present invention is designed to maximize the force applied to the system while at the same time minimizing the size (particularly in the axial direction) of the control device so that it may be incorporated into existing automobile engine housings. Toward this end, in general, the timing control of the present invention utilizes the load and drag of the cam shaft to normally maintain the control mechanism in the home or retarded position. Upon engine ignition, or upon the attainment of other prescribed parameters, the oil pressure of the lubricating system is utilized to advance a unique toggle linkage between the cam shaft and crankshaft to an "advance" position in which the cam shaft is rotated slightly relative to the crankshaft. Neither the crankshaft nor the cam shaft require significant modification thereto, as the control device is merely mounted to the end of the cam shaft and connected to the crankshaft by a chain, belt or gear. Further, the device is relatively frictionless. In general, the timing device of the present invention is made a part of the sprocket which receives the driving force from the crankshaft. The timing device includes an inner plate secured to the end of the cam shaft and having at least one passageway therethrough in communication with lubrication system of the engine. An outer plate surrounds the periphery of the inner plate in rotatably adjustable relation thereto and, of course, is directly connected in synchronous driven relation to the crankshaft. The heart of the present invention resides in a linking spider which is mechanically connected between the inner plate and outer plate through a toggle linkage which transmits the driving force from the outer plate to the inner plate. In the retard position, the drag forces exerted on the cam shaft through the spider to the inner plate by means of the aforesaid connecting linkage provides a pull on the linkage tending to keep the inner plate in the normal or "retard" position. However, at low speeds, oil pressure is exerted axially against a relatively large surface in or on the connecting spider to move the spider axially from its normal position. This axial movement of the spider causes a displacement of the connecting toggle linkage, thereby arcuately altering the relationship between the cam shaft and the crankshaft to the "advance" position.
The hydraulic pressure which actuates the spider may be controlled by a centrifugal valve which is closed causing the pressure to build up during low speeds, then opens to bleed off the pressure during high speeds; or it may be controlled by a solenoid operated hydraulic valve to cause buildup of oil pressure or to bleed off oil pressure responsive to a computer or microprocessor which is continuously monitoring various engine characteristics such as vacuum, engine speed, or other characteristics, which characteristics may be compared to control the opening and closing of the hydraulic valve more closely.
It is therefore an object of the present invention to provide a cam shaft timing control of the type described which is simpler in design and more reliable than previously known devices.
It is another object of the present invention to provide a cam shaft timing control of the type described which utilizes the load and drag on the cam shaft to normally bias the control device to one position.